H3C-CH2-CH2-CH3
ion-ion bonds: not an ion
ion-dipole bonds: not an ion and no dipole
dipole-dipole bonds: butane is nonpolar, so no dipole
Hydrogen bonds: does not contain H bonded to F,O, or N
therefore the only intra-molecular bonds remaining are the weakest of the weak - london dispersion forces (aka Van Der Waals). These are randomly induced dipole attractions that happen when the electrons that move around randomly just happen to have a higher concentration at one end of the molecule. This causes dipoles to form in adjacent molecules, which induce dipoles in molecules next to them. these forces are very weak, but still play a part in raising the boiling point of butane.
